The present invention relates to a data back-up system using a nonvolatile READ/WRITE memory and, more particularly, to a data back-up system advantageously applicable to a handy terminal or a portable data terminal and capable of preventing data stored in the terminal from being lost.
In a handy terminal or a portable data terminal, a data back-up system for the protection of stored data has customarily been implemented by a volatile memory (RAM (Random Access Memory)) backed up by a battery or a nonvolatile memory (FROM (Flash Read Only Memory) not needing battery back-up.
However, the problem with the conventional data back-up system using a volatile memory backed up by a battery is that the output of the battery decreases due to aging and low temperature, and the battery is apt to bodily come off due to a shock or impact or defective mounting. Any defect of the battery supporting the back-up system directly translates into defective back-up and causes data stored in the terminal to be lost. The data back-up system using a nonvolatile memory has a drawback that a long period of time is necessary for data to be updated (deletion and writing) even if the system is supported by a flash system or similar special software. Another problem with the nonvolatile memory type system is that the processing of the special software occupies a substantial part of a controller playing the role of a CPU (Central Processing Unit). This prevents another processing from being executed until all the necessary data have been written to the nonvolatile memory.